Photoelectrophoretic imaging system

ABSTRACT

A photoelectrophoretic imaging system is disclosed wherein the injecting and blocking electrodes are both transparent. Both electrodes are drum structures and the light image used to activate the photoelectrophoretic ink is projected to the ink from two sides through each transparent electrode.

United States Patent Inventor Kallis II. Mannik Rochester, N.Y. Appl. No. 836,420 Filed June 25, 1969 Patented Oct. 5, I971 Assignee Xerox Corporation Rochester, N.Y.

PHOTOELECTROPI-IORETIC IMAGING SYSTEM 8 Claims, 4 Drawing Figs.

US. Cl 355/3,

7 355/II,355/l7 Int. Cl G03g 15/00 Field ofSearch 355/3, 7,

[5 6] References Cited UNITED STATES PATENTS 3,383,993 5/1968 Yeh 355/3 Primary ExaminerSamuel S. Matthews Assistant Examiner-Monroe H. Hayes Attorneys-James J. Ralabate, Michael H. Shanahan and David C. Petre ABSTRACT: A photoelectrophoretic imaging system is disclosed wherein the injecting and blocking electrodes are both transparent. Both electrodes are drum structures and the light image used to activate the photoelectrophoretic ink is projected to the ink from two sides through each transparent electrode.

PATENTED um 5m SHEET 1 BF 2 INVENTOR. KALLIS H. MANNIK ATTOQNEY PATENTED new 5 I97! SHEET 2 [1F 2 FIG. 3

FIG. 4

PHOTOELECTROPI-IORETIC IMAGING SYSTEM BACKGROUND OF THE INVENTION This invention relates to imaging systems and in particular to an improved photoelectrophoretic imaging system.

A detailed description of the photoelectrophoretic imaging process is given in US. Pat. Nos. 3,384,488, 3,384,566, and 3,383,993. Images are formed by the process using an ink or imaging suspension composed of an insulating liquid carrier having photosensitive particles suspended within it. An image is created by placing the ink between injecting and blocking electrodes, one of which is transparent, exposing the ink to a light image through the transparent electrode and establishing an electric field across the ink. One theory of operation is that the ink' particles carry a net charge while in suspension and therefore are attracted to the electrodes by the field. The particles attracted to the injecting electrode experience an apparent charge exchange with the electrode when exposed to a light image. These particles migrate from the injecting electrode to the blocking electrode creating a positive image on the injecting electrode and a negative image on the blocking electrode. The blocking electrode is so named because it has the ability to minimize charge exchange between itself and the ink particles. This ability of the blocking electrode is obtained, in one manner, by coating the electrode with an electrically insulating material.

' The photoelectrophoretic process is either monochromatic or polychromatic depending upon whether the particles in the ink or imaging suspension are sensitive to the same or different portions of the light spectrum. A full color system is obtained, for example, by using cyan, magenta and yellow particles which are sensitive to red, green and blue light respectively.

The quality of the images produced by the photoelectrophoretic process is dependent upon the number of particles caused to migrate between the electrodes. The number of migrating particles is established by the intensity of the light to which the particles are exposed and the strength of the electric field. An increase in the light energy, however, does not always result in a proportional increase in image quality. The reason, at least in part, is that the ink particles are generally opaque and act to shield light from one another. The problem varies with variations in the density of the particles within the carrier and with variations in the quantity of ink placed between the electrodes. In any event, the particles closest to the transparent electrode tend to absorb the majority of the light energy and thereby shield the particles deeper within the volume of the ink from the light. These shielded particles are not as likely to experience a charge exchange with the injecting electrode, other particles or other charge carriers and therefore cannot be expected to participate in the image forming migration. The consequences include a lower image quality at slower image forming speeds.

Accordingly, it is an object of this invention to improve the photoelectrophoretic imaging system by overcoming the above noted difficulties. Specifically, it is an object of the invention to expose the photoelectrophoretic ink from two directions and thereby increase the speed of image formation and improve the image quality.

. Yet another object of the present invention is to increase the quantity of ink particle migration in the photoelectrophoretic process.

Furthermore, it is an object of the invention to employ both transparent injecting and transparent blocking electrodes in a photoelectrophoretic system in order to increase the quantity of ink particles exposed to a light image. Likewise, it is also an object of the invention to devise means for simultaneously projecting images to opposite sides of a photoelectrophoretic ink.

DESCRIPTION OF THE DRAWINGS The advantages of the present improved imaging systems will become apparent upon consideration of the description of the invention especially when taken in conjunction with the accompanying drawings which are:

FIG. 1 is a schematic illustration of a front elevational view of a photoelectrophoretic system according to the present invention;

FIG. 2 is a schematic illustration of a front elevational view of a second embodiment of the present invention;

FIG. 3 is a schematic illustration of a sectional view of the present invention taken along lines 3-3 in FIG. 2 plus additional apparatus; and

FIG. 4 is a schematic illustration of a sectional view of the present invention taken along the lines 55 in FIG. 3.

DESCRIPTION OF THE INVENTION The photoelectrophoretic imaging systems shown in the figures include the injecting electrode 1 and the blocking electrode 2 which are shaped in the form of drums or rollers. The drums l and 2 are supported for rotation and are positioned relative to one another so as to contact at their peripheries thereby forming the nip 3. A positive image is formed on the peripheral surface of the injecting electrode 1 from the photoelectrophoretic ink or imaging suspension 4 placed between the electrodes at the nip 3. The electrodes are coupled to the battery or voltage source 6 and when the switch 7 is closed an electric field is established between the electrodes. Both the electrodes are transparent and the ink 4 between the electrodes is exposed to a light image projected through each transparent electrode. A full frame image is created on the surface of the injecting electrode drum 1 by closing switch 7 to set up the electric field, by projecting light through the two transparent electrodes to the ink 4 and by rotating the two drums.

The drum or roller configuration of the electrode is not exclusive. One or both of the electrodes may be in the shape of a flat plate or other configuration. However, it is common to design the electrodes so they contact one another over a limited area such as with nip 3. Also, it is common to support the electrodes so one is moved relative to the other thereby forming an image line by line at the nip or contact area between the electrodes. The drum configuration is employed in the present case because it lends itself to a continuous image forming operation.

The injecting electrode drum 1 is made up of a cylinder of electrically conductive glass commercially available under the name NESA glass. The NESA glass consists of an optically transparent glass 9 overcoated with a thin optically transparent layer of tin oxide 10; The blocking electrode drum 2 is also made up of a cylinder of optically transparent NESA glass. However, in the case of drum 2, the optically transparent tin oxide 10 is itself overcoated with an optically transparent, highly insulating material 14, e.g. polyethylene.

The drums l and 2 are positioned with their axes of rotation 16 and 17 parallel and with their peripheral surfaces contacting. The space between the drums as illustrated in the drawings is shown merely to identify the location of the ink 4 between the drums. During imaging, the electrically insulating ink 4 separates the two drums from each other at the nip 3, the thickness of which is generally in the order of 1 mil.

FIGS. 1-2 illustrate two different embodiments for the illuminating means for exposing two sides of the photoelectrophoretic ink 4 to a light image. In FIG. I, a light image of an original 18 is projected to two sides of the ink 4 through the two transparent electrodes. The original 18 is a transparency supported by the frame 19 and illuminated from behind by the lamp 20. A light image of the original is directed onto the beam splitter 21 of a well-known type having a partially reflective and partially transparent surface capable of both transmitting and reflecting light. The light image reflected by the beam splitter is collected by lens 22 and focused onto the nip 3 through the injecting electrode 1 after first being reflected off the surface of mirror 23. The light image transmitted by the beam splitter is collected by lens 24 and focused onto the nip 3 v mirror 26.

The light image projected through the injecting electrode is an optically right reading positive image of the original 18 because the light image is reflected off two mirror surfaces namely the reflective surfaces of beam splitter 21 and mirror 22. The light image projected through the blocking electrode is a wrong reading positive image (or mirror image) of the original 18 because only one reflecting surface is involved in its projection to the nip 3 which is the surface of mirror 26. The right and wrong reading images are required at the two sides of the nip 3 in order to have the entire volume of ink 4 within the nip subjected to a consistent light pattern or image. The right reading light image projected through the injecting electrode enables a wrong reading positive image to be produced on the surface of the injecting electrode. A right reading positive image is obtained upon transferring the image formed on the injecting electrode to a record sheet.

For the purpose of the present description, the nip 3 can be considered to have length only which is to say it is a line extending the width of the drums l and 2. Therefore, in order to produce a full frame image of the original 18, the drums are rotated in opposite directions and the original is moved in a direction perpendicular to the plane of FIG. 1. The speed at which the original is moved is substantially the same speed as the relative speed between the drums. To form images in sizes other than the foregoing one to one ratio, the optics and relative speed of the various moving parts must be altered. However, regardless of the size, the speed of the original 18 is generally equal to or a multiple of the speed of the drums and is said to move synchronously with the movement of the drums.

The illuminating means shown in FIG. 2 includes the object drum 27, mirror 28, beam splitter 29, lenses 31 and 32 and mirrors 33, 34, 35, and 36. The original 38 is mounted on the peripheral surface of object drum 27 with the image to be reproduced facing inward. A light source is directed onto the original 38 as indicated by the arrows 39. A light image of the original is reflected off the surface of mirror 28 to the beam splitter 29. The light image is transmitted through the beam splitter to lens 31 which, along with mirror 36, focus the light image to the nip 3 through the transparent injecting electrode 1. The surfaces of mirror 28 and the surface of mirror 36 cause an even number of reflections therefore the light image projected through the injecting electrode is a positive right reading image.

The light image reflected by the beam splitter 29 is reflected off mirror 33 and focused by lens 32 and mirrors 34 and 35 onto nip 3 through the transparent blocking electrode 2. This image projected through the blocking electrode undergoes an odd number of reflections and is consequently a positive wrong reading image of the original 38. (The surface of mirror 28, beam splitter 29, and mirrors 33, 34, and 35 cause the five or odd number of reflections of the light image.)

The object drum 27 is supported for rotation and is rotated synchronously with the electrode drums 1 and 2. The mirror 28 and the other mirrors and lenses are held stationary so the full frame image of the original is produced on the surfaces of the electrodes as the object drum and the electrode drums rotate through the appropriate angles.

Turning now to FIG. 3 the ink 4 is applied to the injecting electrode by the inking roller 56. A reservoir of ink is dispensed from tank 57 onto the inking roller which in turn applies the ink to the injecting electrode drum 1. As the ink passes through the nip 3, it is exposed to the light image and subjected to the electric field, a positive wrong reading image is formed from the ink particles 58 remaining on the surface of the injecting electrode and a negative image is formed from the ink particles 59 that migrate to the blocking electrode. The positive image is wrong reading for the reasons explained earlier and is a right reading image when viewed on the record sheet 61 to which it is transferred as the injecting electrode 1 rolls past the transfer roller 62. The cleaning rollers 63 and 64 are felt, cotton, fur or the like brushes which clean the surface of the electrodes as they rotate thereby permitting new images to be formed on the electrodes during subsequent revolutions. The drum configuration for the electrodes therefore readily lends itself to a continuous image forming operation. In addition, using a drum configuration for at least one of the electrodes allows relatively simple illuminating means to be employed for two sided exposure of the ink because the light image can be projected from the axis of a drum to the nip.

F IG. 4 illustrates the object drum 27 of FIG. 2. The original 38 is mounted on the inside surface of drum 27 with the indicia thereon to be reproduced facing inward. The original is flooded with light produced by the maps 66 and 67. The lamps and mirror 28 remain stationary as the drum rotates thereby providing a line by line scan of the original. The object drum moves synchronously with the electrode drums to permit formation of the image on the electrode in a corresponding line by line sequence.

What is claimed is:

l. Photoelectrophoretic imaging apparatus comprising transparent injecting and blocking electrodes having means for coupling to a voltage source for establishing an electric field therebetween,

illuminating means for exposing the two sides of an imaging suspension positioned between said transparent electrodes to a light image whereby an image is formed from the imaging suspension exposed to the light image and subjected to an electric field.

2. The apparatus of claim 1 wherein said illuminating means includes means to project right reading and wrong reading light images through said injecting and blocking electrodes to an imaging suspension therebetween.

3. The apparatus of claim 1 wherein at least one of said electrodes is a drum supported to contact the other electrode at a nip and for movement relative thereto and wherein said illuminating means includes means for projecting a light image to said nip through said injecting and blocking electrodes.

4. The apparatus of claim 1 wherein said electrodes include drums contacting at a nip and supported for rotation and wherein said illuminating means includes projection means for projecting a light image of an original to said nip through said injecting electrode and through said blocking electrode.

5. The apparatus of claim 1 wherein said electrodes include drums supported for rotation and contacting at a nip and wherein said illuminating means includes means for supporting an original,

first means for projecting a light image of the original to said nip through said blocking electrode, and

second means for projecting said light image to said nip through said injecting electrode.

6. The apparatus of claim 1 wherein said electrodes include drums supported for rotation and for contacting at a nip and wherein said illuminating means includes a beam splitter for reflecting and transmitting light images,

first mirror means positioned to reflect a light image transmitted through said beam splitter to said nip,

second mirror means positioned to reflect a light image reflected by said beam splitter to said nip, and

support means for positioning an original relative to said beam splitter such that a light image of the original is reflected and transmitted by the beam splitter to said first and second mirror means and for moving the original substantially synchronously with the movement of said electrodes.

7. The apparatus of claim 1 wherein said electrodes include drums supported for rotation and for contacting at a nip and wherein said illuminating means includes an object drum for carrying an original supported for rotation substantially synchronously to the rotation of said electrodes,

first projection means for projecting a right reading light image of an original to said nip through said injecting electrode, and

suspension applied between the nip of the electrodes to a light image to fonn a positive image on one of the electrodes and a negative image on the other electrodes from the imaging suspension exposed to a light image and subjected to an electric field,

means for transferring the positive image from the electrode on which it is formed, and

means for cleaning the surface of the electrodes for the subsequent formation of images thereon. 

1. Photoelectrophoretic imaging apparatus comprising transparent injecting and blocking electrodes having means for coupling to a voltage source for establishing an electric field therebetween, illuminating means for exposing the two sides of an imaging suspension positioned between said transparent electrodes to a light image whereby an image is formed from the imaging suspension exposed to the light image and subjected to an electric field.
 2. The apparatus of claim 1 wherein said illuminating means includes means to project right reading and wrong reading light images through said injecting and blocking electrodes to an imaging suspension therebetween.
 3. The apparatus of claim 1 wherein at least one of said electrodes is a drum supported to contact the other electrode at a nip and for movement relative thereto and wherein said illuminating means includes means for projecting a light image to said nip through said injecting and blocking electrodes.
 4. The apparatus of claim 1 wherein said electrodes include drums contacting at a nip and supported for rotation and wherein said illuminating means includes projection means for projecting a light image of an original to said nip through said injecting electrode and through said blocking electrode.
 5. The apparatus of claim 1 wherein said electrodes include drums supported for rotation and contacting at a nip and wherein said illuminating means includes means for supporting an original, first means for projecting a light image of the original to said nip through said blocking electrode, and second means for projecting said light image to said nip through said injecting electrode.
 6. The apparatus of claim 1 wherein said eleCtrodes include drums supported for rotation and for contacting at a nip and wherein said illuminating means includes a beam splitter for reflecting and transmitting light images, first mirror means positioned to reflect a light image transmitted through said beam splitter to said nip, second mirror means positioned to reflect a light image reflected by said beam splitter to said nip, and support means for positioning an original relative to said beam splitter such that a light image of the original is reflected and transmitted by the beam splitter to said first and second mirror means and for moving the original substantially synchronously with the movement of said electrodes.
 7. The apparatus of claim 1 wherein said electrodes include drums supported for rotation and for contacting at a nip and wherein said illuminating means includes an object drum for carrying an original supported for rotation substantially synchronously to the rotation of said electrodes, first projection means for projecting a right reading light image of an original to said nip through said injecting electrode, and second projection means for projecting a wrong reading light image of an original to said nip through said blocking electrode.
 8. Photoelectrophoretic imaging apparatus comprising transparent injecting and blocking electrode drums contacting at a nip and supported for rotation and having means for coupling a voltage source to establish an electric field therebetween, inking means for applying an imaging suspension between the nip of said electrodes, illuminating means for exposing the two sides of an imaging suspension applied between the nip of the electrodes to a light image to form a positive image on one of the electrodes and a negative image on the other electrodes from the imaging suspension exposed to a light image and subjected to an electric field, means for transferring the positive image from the electrode on which it is formed, and means for cleaning the surface of the electrodes for the subsequent formation of images thereon. 